1. Field of the Invention
The present invention consists of a container made of heat-moulded plastic material and designed for fizzy drinks. More paricularly, the present invention concerns a container designed for fizzy drinks; it has a heat-moulded lid which is joined to the body of the container, and which can resist the variations in pressure that the fizzy drink may create in various environmental conditions.
2. Description of the Prior Art
As already known, glass bottles closed with crown caps clamped to the underside of the ring-shaped protruberance on the neck of the bottle are used for the distribution of fizzy drinks. These containers are extremely hygienic and stable, and they satisfy all the requirements of the field, but they have the disadvantage of being fragile, heavy, and expensive. In order to avoid these disadvantages, especially for drinks to be consumed immediately and for single doses, firms have introduced disposable metal containers which are convenient to use, easy to store in a warehouse, and of good appearance, especially those which have tear-off openings with ring-pull levers pressed down on to the lid of the container.
These containers, apart from being relatively expensive, are not free from certain physiological and hygiene risks, or organolectic ones, due to the use of aluminum or thin paint layers polymerized in place, employed especially in containers in iron bands.
Well known also are containers made of thermoplastic material with self-sealed covers made of metal or thermoplastic material. These containers have been widely used to contain drinks and non-fizzy food products in so far as it is possible to produce them in thermoplastic resins suitable for foodstuffs, i.e. resins which do not liberate substances harmful to human health whether on their own account resulting from usual additives such as plastifiers or accelerators added during the production phase. However, their reduced breaking strain under traction and their low modulus of elasticity make it difficult to produce containers in plastic material suitable for fizzy drinks, especially saturated at 25.degree. with 4 Kg/cm.sup.2 of CO.sub.2, which may increase to 8 Kg/cm.sup.2 when, for environmental conditions, one may find temperatures of up to 40.degree. C.
Under these conditions, the material may be placed under an increased strain if one cannot provide an area of expansion so placed that it does not disturb the stability of the individual container and also that of the stored quantities in the warehouse. Furthermore, it is known that, across the thin walls of the thermoplastic material, there is an osmotic migration, particularly of CO.sub.2, as a result of the enormous differences of partial pressure of the same above the liquid and in the area surrounding the container. Therefore, CO.sub.2 is continually flowing into the environment, so the pressure at the surface of the liquid is reduced.